62 Illinois State Laboratory of Natural History. 



retraction, no trace of them being commonly perceptible from 

 without. These probably represent the modified setse of the 

 prostate glands in Acanthodrilus, in which genus they are de- 

 scribed as projecting fasicles of ornamented and more or less 

 retractile setse. The muscular duct of the prostate, with its ac- 

 companying setse, does not, therefore, as in Acanthodrilus, con- 

 stitute " un veritable penis," the secretion of the jirostates being 

 in Diplocardia discharged independently of that of the seminal 

 vesicles. This complete separation of the two sets of glands 

 calls for another arrangement by which the secretions may be 

 mingled, and this we have in the copulatory fossae and the re- 

 lations of the apertures of the various ducts to them. (See 

 figure.) Another difference between the two genera is in the 

 number of spermathecas: Diplocardia has three pairs, one each 

 in somites 7, 8, and 9, while Acanthodrilus has two pairs, one 

 each in somites 8 and 9. With regard to the subneural blood 

 vessel of earthworms, Mr. W. B. Benham (loc. cit.) says, 

 " There is a sub-neural trunk in all forms, except Perichaeta, 

 Pleurochseta, Pontodrilus [and Microchaeta]." From this we 

 must infer that Acanthodrilus possesses this trunk; but in 

 Diplocardia it is wanting, as are also the supraneural vessels. 

 In the imperfect oesophagus of Diplocardia we may perhaps 

 find still another differerence. This division of the alimentary 

 canal is represented in Mr. Beddard's figure of Acanthodrilus 

 layardi as a slender tube rather longer than the pharynx. It 

 is represented as longer than the pharynx also in M. Perrier's 

 A. ungulatus. Finally, the two genera differ in the character 

 of the dorsal vessel. Some species of Acanthodrilus have been 

 described as having the dorsal trunk divided in a few of the an- 

 terior somites, but in no description which I have seen has men- 

 tion been made of a dorsal vessel made up of two tubes through- 

 out its length, as ill' the case in the genus here described. Not- 

 withstanding these differences, Diplocardia seems to the writer to 

 be more closely related to Acanthodrilus than to Digaster. The 

 position of the nephridiopores opposite the inner ])airs of setju, 

 and the two muscular gizzards in the latter genus, render it very 

 distinct from either of the others, and makes a comi)arison with 

 Diplocardia unnecessary. The species of Acanthodrilus have 

 been o))tained from the East India Islands, from Madagascar, 



